Yes, as Jeff notes I have replaced more coils in the past two years then the last 20 combined. It seems like the lifespan has been reached on coils built in the 1980's. They are developing small hairline cracks that are almost impossible to see (unless you see the spark jump from them with the motor running).
Just as a matter of course, and since this is just a twin, I would consider replacing both the coils "just because".
I wouldn't go with OEM (too expensive), instead I have been opting for Sierra coils (list at about 20 bucks each) and they are superior to OEM coils for Merc portables (2 cylinder models)...